As this kind of silicon single crystal pulling-up device, there has been conventionally disclosed a pulling-up device (for example, Japanese Examined Patent Application Publication No. Sho 57-40119) in which a quartz crucible in which silicon melt was amassed is stored in a chamber and a heat shielding member was inserted between the outer peripheral face of a silicon single crystal rod and the inner peripheral face of the quartz crucible so as to surround the silicon single crystal rod. The heat shielding member in the device is composed so that it surrounds the outer peripheral face of the silicon single crystal rod which is pulled up and its lower end is situated upward at an interval from the surface of the silicon melt, it has a tube portion which shields radiant heat from a heater, and the heat shielding member introduces smoothly inactive gas which flows down between the outer peripheral face of the silicon single crystal rod and the inner peripheral face of the tube portion. In the pulling-up device, it is prevented by shielding radiant heat from the inner peripheral wall of a quartz crucible exposed that radiant heat reaches at the outer peripheral face of the silicon single crystal rod; therefore the solidification of the silicon single crystal rod under pulling-up is accelerated and the silicon single crystal rod is designed to be speedily cooled.
Further, as this kind of silicon single crystal pulling-up device, there is disclosed a device in which a tube portion is formed as a multilayer structure having a mother member such as graphite which has heat resistance at a temperature range of the radiant heat and a covering material such as quartz which covers the face at the silicon single crystal rod side of the mother member and has a smaller radiation coefficient than that of the mother member (for example, Japanese Patent Laid-Open Publication No. Hei 08-325090). Since the mother member having a larger radiation coefficient was covered with a covering member having a smaller radiation coefficient than that of the mother member in the heat shielding member thus composed, the shielding effect of the radiant heat of a crucible and a heater to the silicon single crystal rod can be improved. As a result, the pulling-up speed of the silicon single crystal rod by acceleration of cooling can be increased and the productivity of the silicon single crystal rod can be improved.
On the other hand, as causes for lowering an yield in steps of producing a semiconductor integrated circuit, there are mentioned the fine faults of an oxygen precipitate being the nuclei of an oxidation-induced Stacking fault (Oxidation-induced Stacking Fault (hereinafter, referred to as OSF)), a particle originated in crystal (Crystal Originated Particle (hereinafter, referred to as COP)) or the existence of invasive type dislocation (Interstitial-type Large Dislocation (hereinafter, referred to as L/D)). OSF is the cause of trouble such as the increase of leak current of a device which is prepared by introducing fine faults being the nuclei during crystal growth and actualizing them in the thermal oxidation step and the like when a semiconductor device is produced. Further, the COP is a pit originated in a crystal which appears on the surface of a wafer when a silicon wafer after mirror polishing was rinsed with a mix solution of ammonia and hydrogen peroxide. When the wafer is measured with a particle counter, the pit is also detected as an optically scattered fault together with a natural particle.
The COP becomes a cause for deteriorating, for example, the aging property of insulation breakage of an oxidized film (Time Dependent dielectric Breakdown, TDDB), the property of pressure resistance of an oxidized film (Time Zero Dielectric Breakdown, TZDB) and the like. Further, when the COP exists on the surface of a wafer, level difference is generated at the wiring step of a device and may be possibly a cause for disconnection. Further, it is also a cause for leak and the like at an element separation portion and the yield of a product is lowered. Further, the L/D is also called as a dislocation cluster, or is also called as a dislocation pit because a pit is generated when the silicon wafer which generated the fault is immersed in a selective etching solution in which hydrofluoric acid is a main component. The L/D is also a cause for deteriorating electrical properties, for example, leak property, isolation property and the like. As a result, it is required that the OSF, COP and L/D are reduced from a silicon wafer which is used for production of a semiconductor integrated circuit.
The production processes of a silicon single crystal rod based on the Voronkov theory are disclosed in order to cut out silicon wafers without faults having not the OSF, COP and L/D (for example, U.S. Pat. No. 6,045,610 and Japanese Published Patent Application No. Hei 11-1393). In the Voronkov theory, when the silicon single crystal rod is pulled up at a high speed, a zone [V] in which the agglomerate of hole-type point faults exists predominantly is formed in the inside of the silicon single crystal rod, and when the silicon single crystal rod is pulled up at a low speed, a zone [I] in which the agglomerate of interstitial silicon-type point faults exists predominantly is formed in the inside of the silicon single crystal rod. Accordingly, the above-mentioned production process can produce a silicon single crystal rod comprising a perfect zone [P] in which the agglomerate of the point faults does not exist, by nearly homogenizing the distribution of temperature gradient to a diameter direction in the axial direction of the silicon single crystal rod by pulling up the silicon single crystal rod at an optimum speed.
However, since the quantity of radiant heat from the outer peripheral face of the silicon single crystal rod which is pulled up from silicon melt is much in the heat shielding member in the silicon single crystal pulling-up device shown in Japanese Published Patent Application No. Hei 08-325090, the temperature gradient to an axis direction at the outer peripheral portion of the silicon single crystal rod is higher in comparison with the temperature gradient to an axis direction at the center of the silicon single crystal rod and there is a problem that the distribution of temperature gradient to a diameter direction in the axial direction of the silicon single crystal rod cannot be homogenized. In particular, when the enlargement of the diameter of the silicon single crystal rod proceeds, it is anticipated that the difference of the temperature gradient to an axis direction between the central portion and the outer peripheral portion of the above-mentioned silicon single crystal rod is further enlarged. Consequently, there has been a fear that thermal stress based on the above-mentioned difference is generated in the silicon single crystal rod and the silicon single crystal rod without faults cannot be obtained.
It is the object of the present invention to provide the heat shielding member of a silicon single crystal pulling-up device which obtains a silicon single crystal rod without faults by contracting the difference of the temperature gradient to an axis direction between the central portion and the outer peripheral portion of the silicon single crystal rod by intercepting the abrupt lowering of temperature of the outer peripheral face of the lower portion of the silicon single crystal rod under pulling-up from a silicon melt.